A technique known as deformation processing has been developed to improve the strength of Cu-V, Cu-Nb, Cu-Ta, Cu-Fe, Cu-Cr, etc. two phase materials to provide a high strength, high conductivity material for superconducting and other electrical current carrying applications. This technique involves producing a billet of a two phase material (Cu phase and V, Nb, etc. phase) by conventional casting or powder metal processes and then deforming the billet to a significant extent to codeform the two phases present. The amount of deformation is characterized by the parameter, .eta., which is defined as the natural logarithm of the ratio of the original area, A.sub.o, of the billet to the final area, A.sub.f, of the deformed billet; i.e., .eta.=1n((A.sub.o /A.sub.f). As deformation increases, the value of .eta. rises from 0 up to as high as 10 to 12. A value of .eta. of only 6 represents a very large deformation; e.g., corresponding to reduction of a 1 inch diameter bar to a 0.05 inch diameter wire. Successful deformation of the billet requires that both of the phases present in the billet codeform (deform concurrently) as the cross-sectional area is reduced.
Deformation processing has been most successfully applied to cubic alloy systems, such as the Cu-V, Cu-Nb, Cu-Ta, Cu-Fe, Cu-Cr, etc. systems referred to above as well as to Al-Nb, Al-Ta, and Ni-W systems, wherein one phase has a body centered cubic (bcc) crystal structure and the other phase has a face centered cubic (fcc) crystal structure. In these systems, the bcc phase is observed to change in cross-sectional shape during deformation from a nearly cylindrical morphology to a ribbon morphology which is important for strength attainment purposes. Deformation processing has been less successful in providing strength improvements in cubic alloy systems, such as Cu-Ag, wherein both phases have fcc crystal structures. For example, deformation processed Cu-Ag alloy systems have exhibited a strengthening effect that is less than that observed in the bcc/fcc alloy systems described above. The lesser strengthening effect has been attributed to the failure to develop the desired ribbon morphology in fcc phases present in the Cu-Ag billet upon mechanical deformation thereof.
Titanium alloys have been developed to take advantage of the high mechanical strength and low density of titanium and are in widespread use in the aerospace, transportation, sporting goods, and chemical processing industries. The presence in titanium of an allotropic hexagonal (alpha).fwdarw.cubic (beta) phase transition at elevated temperatures has allowed a large number of alloys to be developed based upon control of the relative amounts of the two phases through alloying additions (i.e., alpha or beta formers). The microstructure of the most commonly used alloys now in service consists of a mixture of the alpha and the beta phases, together with various intermetallic precipitates formed as a consequence of solution and aging heat treatments to which the alloy is subjected. Examples of near-alpha and alpha plus beta alloys in widespread use include the well known Ti-8%Al-1%Mo-1%V and Ti-6%Al-4%V alloys where the alloyant percentages set forth are in weight percent. These alloys possess relatively high strength and reasonable ductility at room and elevated temperatures; e.g., greater than 850 Mpa ultimate tensile strength and 10-15% elongation at room temperature.
Titanium-based metal matrix composites comprising approximately 20 weight % reinforcement filaments in a titanium or titanium alloy matrix have been developed to this same end. However, processes for making these composites involve pressure infiltration, thixocasting, or attrition milling followed by hot isostatic pressing of the attrited material to achieve full density and thus are quite laborious and expensive.
A titanium-based metal matrix composite exhibiting improved mechanical properties and manufacturable by a simpler, more cost effective process would be welcomed in the art of high strength-to-weight materials for structural and other components in such diverse applications as aerospace, transportation, sporting goods and chemical process components.